The present invention relates to a novel and advantageous process for producing aromatic hydroxyl compounds alkylated at the ortho position (hereinafter referred to as ortho-position-alkylated aromatic hydroxyl compounds).
The ortho-position-alkylated aromatic hydroxyl compounds (for example, ortho-position-alkylated phenols) are useful as plastic materials, and a number of techniques have long been known regarding their preparation method.
Catalysts comprising iron, vanadium, manganese, magnesium or the like as the main component used in the preparation of these ortho-position-alkylated aromatic hydroxyl compounds are known. For instance, a method using magnesium oxide as catalyst has been proposed (U.S. Pat. No. 3,446,856), but this method suffers from the disadvantage of being difficult to alkylate the ortho position only because of the formation of abundant by-products, that is, ortho position selectivity is low, resulting in a low yield of the objective compound.
As a solution to this problem, use of a catalyst containing vanadium oxide and iron oxide has been proposed (JP-B-47-37943). This catalyst has high activity and allows reactions to proceed relatively low temperature (300-400xc2x0 C.). The catalyst also produces relatively high ortho-position selectivity. However, this catalyst still fails to provide sufficient ortho-position selectivity for the industrial process to be practicable.
Further, both of the above-mentioned methods suffer the drawback that the alkyl alcohol (such as methanol) used in the reaction tends to decompose during the reaction, generating gases such as CO2, CO, CH4 and H2 in abundance. This causes a reduction in the amount of alkyl alcohol available for reaction with the ortho-position of the aromatic hydroxyl compounds.
U.S. Pat. No. 4,097,411 discloses the recovery of unreacted aromatic hydroxyl compounds, which do not take part in the reaction in the production of the ortho-position-alkylated aromatic hydroxyl compounds, and recycling of the recovered compounds for reuse as starting material. This application, however, is silent on the removal of low-boiling point impurities from the recovered aromatic hydroxyl compounds.
The present invention is designed to provide a process for producing an ortho-position-alkylated aromatic hydroxyl compound in high yield by alkylating the ortho position of an aromatic hydroxyl compound with high selectivity, and also increasing the amount of alkyl alcohol, which is reactable with the ortho position of the aromatic hydroxyl compound.
Thus, the present invention pertains to a process for producing an ortho-position-alkylated aromatic hydroxyl compound by subjecting an aromatic hydroxyl compound and an alkyl alcohol to a gas phase catalytic reaction in the presence of a metal oxide catalyst, said aromatic hydroxyl compound being a mixture of a phenol and ortho cresol, and the amount of ortho cresol in the mixture being 0.6 mole or less per 1 mole of phenol.